Film forming apparatus

ABSTRACT

A process and an apparatus for forming films, up to several microns in thickness, on substrates by the combination of ion implantation and vapor deposition; said apparatus comprising a vacuum chamber, means for transporting a substrate within the vacuum chamber, a first ion source having an accelerating voltage of 500 V to 5 kV and disposed at a first position along the direction of movement of the substrate within the vacuum chamber, a first evaporator disposed at a second position along the direction of movement of the substrate within the vacuum chamber, and a second ion source having an accelerating voltage of 10 kV to 100 kV and disposed at a third position along the direction of movement of the substrate within the vacuum chamber, and optionally further comprising a second evaporator disposed at a fourth position along the direction of movement of the substrate within the vacuum chamber, which may be provided with high-frequency exciting means disposed in a path of release of vapor from the second evaporator toward the substrate for ionizing the vapor, and means for forming an electric field for accelerating the ionized vapor toward the substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process and an apparatus for formingfilms, up to several microns in thickness, on substrates by thecombination of ion implantation and vapor deposition.

2. Description of the Prior Art

It is known to form a film on the surface of various substrates, such assteel plates, tools (drills, tips, bits, etc.) and rollers, to givehigher corrosion resistance or improved hardness to the substrate.

Known film forming processes for this purpose include vacuumevaporation, sputtering and ion plating (U.S. Pat. No. 3,793,179).

The vacuum evaporation process is advantageous in forming films at ahigh velocity but has the drawback that the films formed have pooradhesion to the substrates. For example, when strip steel is coated withaluminum and thereafter subjected to press work or like process, thecoating or film is likely to peel off.

The sputtering process has the serious drawback of forming films at alow velocity.

The ion plating process rapidly forms films which have stronger bondswith the substrates than those provided by the vacuum evaporationprocess, but the bond strength still remains to be fully improved.

On the other hand, the ion implantation process is known as a surfacemodifying technique although it is not a film forming process. By theion implantation process, physical, chemical condition of near-surfacelayer can be modified to a depth of hundreds of angstroms to thousandsof angstroms from the surface.

SUMMARY OF THE INVENTION

The present invention provides a process for forming a film ofpredetermined thickness on a substrate in a vacuum chamber comprisingthe steps of:

(i) activating the surface of the substrate by exposing the surface toions at an accelerating voltage of 500 V to 5 kV,

(ii) forming a base deposition layer on the activated substrate surfaceby vapor deposition, the base deposition layer having a thickness notlarger than the depth to which ions can be implanted in the layer, and

(iii) implanting ions in the deposition layer at an accelerating voltageof 10 kV to 100 kV;

the process, when required, further including

(iv) subjecting, a desired number of times, the resulting depositionlayer to

(v) the step of vapor deposition or ion plating, and/or

(vi) said steps (ii) and (iii),

to form at least one layer over the deposition layer.

The process of the invention includes, for example, the combinations ofsteps (i), (ii) and (iii) only, steps (i), (ii), (iii) and (v), steps(i), (ii), (iii), (v) and (vi), steps (i), (ii), (iii), (v), (vi) and(v), etc. Thus, steps (v) and (vi) need not always be performed or maybe performed alternately. Preferably step (v) is performed when thelayer to be thereby formed has good adhesion to the preceding layer (forexample when the two layers are of the same kind). It is desirable toperform step (vi) when the layer to be thereby formed has poor adhesionto the preceding layer (generally when the two layers are of differentkinds). Steps (ii) and (iii) may be performed at the same time.

The present invention further provides a film forming apparatuscomprising a vacuum chamber, means for transporting a substrate withinthe vacuum chamber, a first ion source having an accelerating voltage of500 V to 5 kV and disposed at a first position along the direction ofmovement of the substrate within the vacuum chamber, a first evaporatordisposed at a second position along the direction of movement of thesubstrate within the vacuum chamber, and a second ion source having anaccelerating voltage of 10 kv to 100 kV and disposed at a third positionalong the direction of movement of the substrate within the vacuumchamber.

The present invention further provides a film forming apparatuscomprising a vacuum chamber, means for transporting a substrate withinthe vacuum chamber, a first ion source having an accelerating voltage of500 V to 5 kV and disposed at a first position along the direction ofmovement of the substrate within the vacuum chamber, a first evaporatordisposed at a second position along the direction of movement of thesubstrate within the vacuum chamber, a second ion source having anaccelerating voltage of 10 kV to 100 kv and disposed at a third positionalong the direction of movement of the substrate within the vacuumchamber, a second evaporator disposed at a fourth position along thedirection of movement of the substrate within the vacuum chamber,high-frequency exciting means disposed in a path of release of vaporfrom the second evaporator toward the substrate for ionizing the vapor,and means for forming an electric field for accelerating the ionizedvapor toward the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a film forming apparatus embodying thepresent invention;

FIG. 2 is a diagram showing another embodiment;

FIG. 3 is a diagram showing another embodiment;

FIG. 4 is a diagram showing an embodiment of apparatus for practicingthe process of the invention;

FIG. 5 is a diagram showing an arrangement for tensile strength testconducted in Example 1;

FIG. 6 is a graph showing the relationship between the dose of argonions and the tensile stress;

FIG. 7 is an image diagram showing the structure of a film formedaccording to the invention; and

FIG. 8 is a graph showing a depthwise ESCA chart of a film obtainedaccording to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a film forming apparatus embodying the invention. A feedroll 3 and a take-up roll 4 (substrate transport means) are providedwithin a vacuum chamber 2. A tape-like substrate T is sent from the feedroll 3 to the take-up roll 4. A first ion source 5, a first evaporator6, a second ion source 7 and a second evaporator 8 are arranged oneafter another along the direction of movement of the substrate T.Indicated at 2a is an evacuating opening in communication with a vacuumpump (not shown).

The first ion source 5 is adapted to accelerate ions of an inertelement, such as Ar or Xe, at a voltage of 500 V to 5 kV to irradiatethe substrate T with the ions, whereby the surface of the substrate iscleaned and activated.

The first evaporator 6 has an electron gun 6a for emitting an electronbeam, by which a deposition material A is heated and evaporated to forma first deposition layer on the substrate T. The thickness of the firstdeposition layer to be formed by the first evaporator 6 is approximatelyequal to the mean range of ion from the second ion source or smaller.For example, when an Al deposition layer formed on a substrate of Fe isexposed to accelerated argon ions at 30 keV, the mean range of the argonions within Al is about 30 nm, so that it is suitable for the initial Aldeposition layer to have a thickness approximately equal to or smallerthan this distance. Thus, it is preferable that the thickness beapproximately equal to the mean range of ion. The thickness of the firstdeposition layer is limited by the kinds of the deposition material andions and ion beam energy. For example, with use of ions of the samekind, the first deposition layer can be thicker when the energy isgreater. Further at the same energy level, use of ions and/or depositionmaterial of smaller mass gives a larger thickness to the firstdeposition layer. Furthermore, the mean range of ion increases with andecreases of the atomic number of the accelerated ion and decreases withan increase in the atomic number, as well as in the density, of thesubstrate. Accordingly the thickness of the initial deposition layer canbe determined suitably in corresponding relation to the above-mentionedinitial thickness setting, in the case of combinations of othermaterials.

The second ion source 7 accelerates ions of an element, such as Ar, Xeor N, at a voltage of 10 kV to 100 kV and implants the ions in thedeposition layer. Owing to a knock-on phenomenon between the implantedions and ions constituting the deposition layer or the substrate, atomsof the substrate and those of the deposition layer become mixed at theinterface between the substrate and the deposition layer, forming acontinuously varying composition (mixed layer) in the vicinity of theinterface. Consequently the deposition layer is bonded to the surface ofthe substrate with high strength.

The second evaporator 8 has the same construction as the firstevaporator 6 and evaporates a material B. When the material B is thesame as the deposition material A, a deposition layer of the samematerial as the preceding deposition layer is subsequently formed, withthe substrate held in the same vacuum, so that the layers aresubstantially equivalent to an integral deposition layer. Thus noproblem arises as to adhesion or bond strength. Consequently a film ofpredetermined thickness can be formed on the surface of the substratewhen the second layer is formed to the desired thickness by vapordeposition. The film has a very strong bond with the substrate surface.On the other hand, if the deposition material B differs from thematerial A but has good adhesion to the material A, a second layer ofdesired thickness may be formed by vapor deposition as when the twomaterials are the same. However, when the material B has poor adhesionto the material A (as is the case with different materials), a vapordeposition layer is formed with a thickness approximately equal to orsmaller than the average sputtering distance of ions in the same manneras when the first deposition layer is formed. Subsequently the feed roll3 and the take-up roll 4 are reversely rotated to reversely transportthe substate T to implant ions in the layer by the second ion source 7and give enhanced bond strength.

When it is desired to avoid reverse transport of the substrate T fromthe viewpoint of continuous operation, a third ion source may beprovided subsequent to the second evaporator 8. Similarly additionalevaporators and ion sources may be provided along the path of movementof the substrate when so desired.

FIG. 2 shows another embodiment 11 of film forming apparatus of thepresent invention. Components 2 to 8 each have the same construction asthe corresponding components of the foregoing apparatus 1 referred to bylike reference numerals. The apparatus 11 of FIG. 2 is characterized bya high-frequency power supply 12 and a high-frequency coil 13 forionizing the deposition material vaporized by the second evaporator 8,and a bias voltage source 14 for accelerating the ionized vapor todeposit the vapor on the substrate T for ion plating.

FIG. 3 shows still another embodiment 21 of film forming apparatus ofthe present invention. The apparatus 21 has a feed roll 24 and a take-uproll 23 which are provided outside a vacuum chamber 22. A tape-likesubstrate T is fed to the vacuum chamber 22 through an inlet portion 22Aattached to the chamber 22 and is sent out from an outlet portion 22B.Components 5 to 8 each have the same construction as the correspondingcomponents of the apparatus 1 of FIG. 1 referred to by like referencenumerals. FIG. 3 further shows a welder 26, a band braker 27, mechanicalvacuum pumps 28, diffusion vacuum pumps 29, a deposition material feeder30, a thickness gauge 31 and a control roll 32. Since the feed roll 24and the take-up roll 23 are disposed outside the vacuum chamber 22, therear end of one substrate T can be connected to the front end of anothersubstate T. Thus rolls of substrate can be treated continuously with avacuum maintained in the chamber 22.

Production examples are given below.

PRODUCTION EXAMPLE 1

A strip steel T, 0.5 mm in thickness and 300 mm in width, was degreasedwith trichloroethylene and acetone for pretreatment. An Al film wasformed on one surface of the strip with use of the apparatus of FIG. 1.

The strip steel T, while being moved at a speed of 1 to 15 m/min, wasexposed by the first ion source 5 to Ar ions accelerated at a voltage of500 V to 5 kV to clean and activate the film forming surface. The stripwas irradiated at a dose of 5×10¹⁵ to 5×10¹⁶ ions/cm².

Next, an Al film was formed on the substrate by the first evaporator 6to a thickness of about 400 angstroms (about 40 nm). The thickness ofthe Al film was so determined as to approximately match the mean rangeof Ar ions in Al at an accelerating voltage of 40 kV, as calculatedbased on the LSS theory (Lindhard-Scharff-Schiott theory) which is wellknown on the field of ion implantation technique.

The film was then exposed by the second ion source 7 to Ar ionsaccelerated at a voltage of 40 kV, at a dose of 1×10¹⁶ to 1×10¹⁷ions/cm².

Finally the Al film was formed to a thickness of 1 μm by the secondevaporator 8.

The 1-μm-thick Al film thus formed on the strip steel had high bondstrength. The catalytic action of Ar ions promoted crystallization ofthe deposited film.

During the film forming operation, the vacuum chamber 2 was maintainedat a vacuum of 10⁻⁴ to 10⁻⁵ torr with use of an oil rotary pump and oildiffusion pump. A 30-kW electron gun 6a was used for the firstevaporator 6, and an 80-kW electron gun 8a for the second evaporator 8.

PRODUCTION EXAMPLE 2

A strip steel T, 0.5 mm in thickness and 300 mm in width, was degreasedwith trichloroethylene and acetone for pretreatment and then coated withTiN on one surface thereof with use of the apparatus of FIG. 1.

The strip steel T, while being moved at a speed of 1 to 15 m/min, wasexposed by the first ion source 5 to Ar ions accelerated at a voltage of500 V to 5 kV, at a dose of 5×10¹⁵ to 5×10¹⁶ ions/cm², whereby the filmforming surface was cleaned and activated.

Next, a Ti film was formed on the substrate by the first evaporator 6 toa thickness of about 800 angstroms (about 80 nm). The thickness of theTi film was so determined as to approximately match the mean range ofnitrogen ions in Ti at an accelerating voltage of 40 kV, as calculatedbased on the LSS theory.

The film was then exposed by the second ion source 7 to nitrogen ionsaccelerated at a voltage of 40 kV, at a dose of about 5×10¹⁷ ions/cm².

Finally a film of TiN having a thickness of 1 μm was formed by thesecond evaporator 8.

The 1-μm-thick TiN film thus formed on the steel strip had high bondstrength.

During the film forming operation, the vacuum chamber 2 was evacuated byan oil rotary pump and oil diffusion pump to maintain a vacuum of 10⁻⁴to 10⁻⁵ torr. A 30-kW electron gun 6a was used for the first evaporator6, and an 80-kW electron gun 8a for the second evaporator 8.

PRODUCTION EXAMPLE 3

A strip steel T, 0.5 mm in thickness and 300 mm in width, was degreasedwith trichloroethylene and acetone for pretreatment and then coated withTiN on one surface thereof with use of the apparatus of FIG. 2.

First, the vacuum chamber 2 was evacuated to a vacuum of the order of10⁻⁶ torr, and nitrogen gas having a purity of at least 99.999% wasintroduced into the chamber to maintain a vacuum of the order of 10⁻⁴torr.

The steel strip T, while being moved at a speed of 10 to 50 cm/min, wasexposed by the first ion source 5 to Ar ions accelerated at a voltage of500 V to 5 kV, at a dose of 5×10¹⁵ to 5×10¹⁶ ions/cm², whereby the filmforming surface was cleaned and activated.

Next, a Ti film was formed on the substrate by the first evaporator 6,having a 10-kW electron gun for heating, to a thickness of 600 to 650angstroms (60 to 65 nm). The thickness of the Ti film was so determinedas to approximately match the mean range of nitrogen ions in Ti at anaccelerating voltage of 30 kV.

The film was then exposed by the second ion source 7 to nitrogen ionsaccelerated at a voltage of 30 kV, at a dose of 7×10¹⁶ to 3×10¹⁷ions/cm².

When Ti was thereafter evaporated by the second evaporator 8 having a30-kW electron gun for heating, a high frequency of 13.56 MHz wasapplied to the high-frequency coil 13 at 500 W to 1 kW from the powersupply 12 to cause a discharge, with a voltage of 500 V to 1 kV appliedto the substrate from the bias voltage source 14.

With the implantation of nitrogen ions, the Ti film formed by the firstevaporator 6 became a Ti-N film as strongly bonded to the steel strip T.The Ti vapor formed by the second evaporator 8 was ionized by thedischarge in the presence of nitrogen gas, forming a Ti-N film over thepreceding Ti-N film. Thus, the Ti-N film was formed on the steel strip Twith high bond strength.

EXAMPLE 1

FIG. 4 is a schematic diagram showing another apparatus for practicingthe film forming process of the invention.

The apparatus consists mainly of a rectangular bucket typemulti-aperture ion source 40, an evaporator 41 with an electron beamgun, a rotary specimen holder 42, a film thickness monitor 43 and avacuum chamber 44. FIG. 4 further shows a substrate (specimen) 45, afaraday cup 46, an ion beam current monitor 47, an insulator 40A, anext. grid 40B, a plasma grid 40C, a gas inlet 40D, an arc chamber 40E, afilament 40F, a backstream electron beam dumper 40G, a magnet 40H and asuppressor grid 40I.

As ion species, nitrogen, carbon, etc. and as materials to beevaporated, boron, aluminum, titanium, silicon, etc. can be provided.The temperature of substrates is controlled by water-cooling theinterior of the specimen holder and heater plate attached to the holder.

The performance obtained is as follows.

(1) Ion beam energy: 2-40 keV

(2) Ion beam current: 100 mA for nitrogen ion

(3) Beam intensity distribution: less than 10% within 4×10 cm area attarge

(4) Electron beam power: 5 kW

(5) Base pressure: of the order of 10⁻⁵ Pa

(6) Holder temperture: R.T.-300° C.

(Pretreatment)

The substrates used were low-carbon steel plates mechanicallymirror-polished by buffing wheel. After ultrasonic cleaning withtrichloroethylene and acetone, the substrates were sputtered by a 10-keVargon ion beam for cleaning the surface.

(Preparation of Specimens)

After a thin aluminum film with a thickness of 300 angstroms was formedon the steel substrate by vapor deposition at room temperature and about1×10⁻³ Pa, argon ion implantation was carried out with a dose of 1×10¹⁶or 1×10¹⁷ ions/cm² at the energy of 30 keV. A mixed layer was formedbetween the steel substrate and the thin film. Aluminum was furtherdeposited on the film to a thickness of 1 μm.

(Mechanical Properties of Specimens)

As shown in FIG. 5, each aluminum-coated substrate 51, 10×50×3.2 mm indimensions, was bonded to two aluminum plates 50 by an epoxy resinadhesive 52. Effective area of the sample test was 1 cm². Tensilestrength test was carried out by pulling the aluminum plates 50.

FIG. 6 shows the relationship between the dose of argon ions and thetensile stress. In the case of comparative specimens prepared by coatingsteel substrates with aluminum only by vapor deposition at 200° C.without ion implantation, the thin aluminum film peeled off from thesubstrate only at a tensile stress of 20-30 kg/cm². The peeling tensilestress for ion-implanted aluminum-coated substrate was 280-340 kg/cm² inthe case of the dose of 1×10¹⁶ ions/cm², and only several percent of thealuminum film peeled off partially. In the case of the dose of 1×10¹⁷ions/cm², the adhesive bond formed broke before the aluminum film peeledoff. The maximum tensile stress of the adhesive bond was in the range of280-340 kg/cm².

The increase of tensile strength is due to the mixed layer which isformed in the thin film-substrate interface by ion implantation as shownin FIG. 7. The mixed layer 61 is produced by direct implantation, recoilimplantation at the surface of the substrate 60, and knock-on to thesubstrate of the vapor material. FIG. 7 shows a newly-formed material62, a vapor 63 such as Ti, Al, Cr or the like, and an ion beam 64 as ofN, C, H or the like.

EXAMPLE 2

A coating layer (TiN) having a thickness of 700 angstroms was formed ona stainless steel substrate in the same manner as in Example 1 byconducting ion implantation and vapor deposition at the same time withuse of Ti and N in the ratio of 1:1. The surface was analyzed by ESCA todetermine the depthwise distribution of elements. FIG. 8, showing theresult, indicates that a mixed layer is formed over a thickness of 500angstroms, with nitrogen and titanium ions incorporated into thesubstrate by implantation and knock-on. Fe which is the main componentof the stainless steel is sputtered in the coating layer. Over thethickness of 400 angstroms from the surface, TiN, a new material, formsa surface layer.

As described above, the film forming process and apparatus of thepresent invention has the advantage of forming films at as high avelocity as the conventional vacuum evaporation process and giving avery strong bond between the film and the substrate surface.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

What we claim is:
 1. A film forming apparatus comprising a vacuumchamber, means for transporting a substrate within the vacuum chamber, afirst ion source having an accelerating voltage of 500 V to 5 kV anddisposed at a first position along the direction of movement of thesubstrate within the vacuum chamber, a first evaporator disposed at asecond position along the direction of movement of the substrate withinthe vacuum chamber, and a second ion source having an acceleratingvoltage of 10 kv to 100 kV and disposed at a third position along thedirection of movement of the substrate within the vacuum chamber.
 2. Afilm forming apparatus as defined in claim 1 wherein a second evaporatoris disposed at a fourth position along the direction of movement of thesubstrate within the vacuum chamber.
 3. An apparatus as defined in claim1 wherein the substrate transporting means comprises a feed roll and atake-up roll for transporting a tape-like substrate.
 4. An apparatus asdefined in claim 3 wherein the feed roll and the take-up roll are bothdisposed within the vacuum chamber.
 5. An apparatus as defined in claim3 wherein the feed roll and the take-up roll are both disposed outsidethe vacuum chamber, and the vacuum chamber is provided with an inletportion and an outlet portion for the tape-like substrate.
 6. A filmforming apparatus comprising a vacuum chamber, means for transporting asubstrate within the vacuum chamber, a first ion source having anaccelerating voltage of 500 V to 5 kV and disposed at a first positionalong the direction of movement of the substrate within the vacuumchamber, a first evaporator disposed at a second position along thedirection of movement of the substrate within the vacuum chamber, asecond ion source having an accelerating voltage of 10 kV to 100 kV anddisposed at a third position along the direction of movement of thesubstrate within the vacuum chamber, a second evaporator disposed at afourth position along the direction of movement of the substrate withinthe vacuum chamber, high-frequency exciting means disposed in a path ofrelease of vapor from the second evaporator toward the substrate forionizing the vapor, and means for forming an electric field foraccelerating the ionized vapor toward the substrate.
 7. An apparatus asdefined in claim 6 wherein the substrate transporting means comprises afeed roll and a take-up roll for transporting a tape-like substrate. 8.An apparatus as defined in claim 7 wherein the feed roll and the take-uproll are both disposed within the vacuum chamber.
 9. An apparatus asdefined in claim 7 wherein the feed roll and the take-up roll are bothdisposed outside the vacuum chamber, and the vacuum chamber is providedwith an inlet portion and an outlet portion for the tape-like substrate.